1. Field of the Invention
The present invention relates to a semiconductor integrated circuit device, and more particularly, it relates to a semiconductor integrated circuit device having a memory circuit and a logic circuit integrated on the same semiconductor substrate. More specifically, the present invention relates to a structure for reducing power consumption in a memory-embedded semiconductor integrated circuit device.
2. Description of the Background Art
A system LSI or a memory-embedded LSI formed by integrating a logic circuit and a memory circuit on the same semiconductor substrate is widely employed. In the memory-embedded LSI, the logic circuit and the memory circuit are interconnected with each other through internal interconnection lines on the semiconductor substrate. The internal interconnection line has a smaller load as compared with an onboard wire, and can transmit signals/data at a high speed with low power consumption. The internal interconnection line provided on the semiconductor substrate is not influenced by pitch condition on a pin terminal, and hence the bit width of data between the logic circuit and the memory circuit can be increased to increase the bandwidth in data transmission.
The gate scale of such a memory-embedded LSI is increased in the trend of system integration for implementing a high-functional system with a small area. Further, improvement of the performance of the memory-embedded LSI is attained by reducing a power supply voltage for reducing power consumption and increasing the processing speed.
When the number of gates (number of transistors) of a logic LSI is increased, the total subthreshold current of the transistors is generally increased to disadvantageously increase power consumption in a standby state.
In order to implement a high-speed operation under a low power supply voltage, the absolute values Vth of the threshold voltages of the transistors must be reduced. When the absolute values Vth of the threshold voltages are reduced, however, the subthreshold current is increased to disadvantageously increase power consumption in the standby state.
When the memory-embedded LSI is applied to a portable equipments, the life of a battery serving as a driving power source is reduced due to power consumption increased in the standby state.